1. Field of the Invention
The present invention pertains to a method and apparatus for separation of suspended matter from a liquid. The method and apparatus more specifically applies to a system wherein the separation is accomplished in a vertical single cell vessel by multiple internal hydrocyclones or cyclonic separators for solids and aeration by sparging tubes which provide gas bubbles within the main vessel to cause coalescing and separation of the remaining suspended matter from the water.
2. General Background
Oil/water and solid separators have been widely used in the oil and gas industry, and in pulp and paper mills, municipal waste treatment facilities, steel mills, food processing plants and electricity generating plants. There is thus an ever present and growing problem of contaminated waste water as a by-product of these various processes, and in particular, water produced in the production of oil and gas wells as well as waste water in the refinement process. Air/gas floatation is the method most commonly used to separate suspended material and oil from water and other liquids. Three basic types of air/gas floataton systems exist: dissolved air or gas; rotor-type disbursed air or gas; and, eductor-type disbursed air or gas systems. The hydrocyclone method also has been applied to the separation of suspended matter from liquids. A typical version of the single cell assembly is disclosed in U.S. Pat. No. 3,986,654. This assembly incorporates a single, horizontal, U-shaped tank through which the fluid to be treated is passed. A gas stream is injected into this tank and percolates through the fluid while the pressure of the fluid is increased. After such pressure is released, the gas breaks out of solutions and attaches itself to any contaminants in the fluid, thereby separating these contaminants from the fluid.
A simplified vertical single cell assembly is disclosed in U.S. Pat. No. 5,080,802 to Cairo, Jr., et al. This assembly incorporates a vertical vessel with an internal riser tube which contains additional coalescing means installed therein through which the fluid to be treated is passed. The riser tubes are in open communication with the fluid at or below the surface. An externally mounted eductor system is used along with a static mixing chamber to mix the contaminated liquid influent and a gas injected into the stream by the eductor before the mixture is released into the internal tube section of the vessel.
Yet another system disclosed in U.S. Pat. No. 4,255,262 to O'Cheskey provides an apparatus which mixes and disburses gas in the form of fine bubbles and liquid in a tank in an attempt to remove contaminants from the liquid flow into the tank. The gas is induced from an upper section of the tank downwardly into the liquid in the tank via a draft tube. The gas induction occurs as a part of the liquid contained in the vessel is recycled back through the individual cells or compartments using a centrifugal pump. The apparatus uses a mechanical skimmer assemble which serves to remove contaminated froth accumulated on the surface of the liquid in the tank.